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Regional Travel Modeling

Regional Travel Modeling. Unit 6: Aggregate Modeling. Puget Sound Regional Council’s travel model. Forecast future travel patterns and conditions within the four counties (King, Kitsap, Pierce, and Snohomish) of the Puget Sound region

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Regional Travel Modeling

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  1. Regional Travel Modeling Unit 6: Aggregate Modeling

  2. Puget Sound Regional Council’s travel model • Forecast future travel patterns and conditions within the four counties (King, Kitsap, Pierce, and Snohomish) of the Puget Sound region • Represents the state of the art for regional travel modeling • Analyze the likely impacts of travel forecasts on the region’s transportation infrastructure and environment • Interacts directly with the land use model (UrbanSim), and it is the primary source of input data for the air quality (EPA Moves) and benefit-cost analysis (BCA) tools * Puget Sound Regional Council (PSRC) is the Seattle region’s MPO

  3. Modeling Framework

  4. Seven basic components • Household vehicle availability • Person trip generation • Trip distribution • Mode choice (passenger travel) • Time of day • Trucks • Vehicle trip assignment

  5. Commercial and Passenger Handled Separately • Truck trips are generated, distributed, and then assigned to specific routes. • There is no truck mode choice model as all travel is assumed to occur via the truck mode. • Uses TAZ-level employment data provided by UrbanSim to estimate truck trip generation. • The truck model converts trucks to passenger car equivalents (PCE) prior to route assignment. • accounts for the fact that large trucks occupy more space on roadways than do passenger cars • important for representing the contribution of truck travel to congestion and overall travel speeds. • light trucks represent 1.0 PCE; medium trucks represent 1.5 PCEs and; heavy trucks represent 2.0 PCEs.

  6. Basic unit: TAZ • Transportation Analysis Zone • 938 in 4 county region • Estimate truck trips at the TAZ level based on employment in that zone

  7. 5 time periods 1) AM Peak Period (6:00 am to 9:00 am); 2) Mid-Day (9:00 am to 3:00 pm); 3) PM Peak Period (3:00 pm to 6:00 pm); 4) Evening (6:00 pm to 10:00 pm); 5) Night (10:00 pm to 6:00 am).

  8. Three truck types • Light Trucks • Four or more tires, two axles and weighing less than 16,000 pounds • commercial vehicles such as taxis, rental cars, school buses, ambulances, etc • Medium Trucks • Six or more tires, two to four axles, and weighing between 16,000 and 52,000 pounds • Heavy Trucks • Double- or triple-unit, having 5 or more axles, and weighing more than 52,000 pounds

  9. Trips estimated from employment • Confidentiality issues result in generally underestimated total employment • Certain kinds of manufacturing that are not included in the PSRC land use model (primarily construction and resources employment) • Ag/forestry/fishing • Mining • Construction • Manufacturing – products • Manufacturing – equipment • Communication, transportation, utility • Wholesale • Retail • Financial, real estate, service (fires) • Government • Education

  10. Trip rates • Attraction and production both estimated from employment using different factors • Only change due to changes in employment • Not transportation system performance • No elasticity of demand with respect to travel cost • Special generators • Ports and warehousing districts • Survey based

  11. External trips • Generated and/or destined for outside the region • 1997 TRANSEARCH data • 2001-2003 SFTA data

  12. Validation • The FASTruck model was validated system wide based on a limited set of truck counts for medium and heavy trucks. • Light-truck travel was validated on a system wide basis to ensure that the assignments of these trucks did not significantly affect the assignments of passenger cars. • The existing FASTruck model does include all non-personal-use vehicles.

  13. Trip destination • Gravity model approach • Closer TAZes attract more trips • Different for each truck class • Estimated from consultant report • SFTA survey • Distributed over the day • From PSRC screenline counts from trucks

  14. Network • Traffic assignment with equilibrium assumption • Congestion effects captured with link performance functions • Only the highway network is used • Recall zone to zone travel • Trucks assigned along with all other traffic • All vehicles on same link travel same speed • Reduce truck speeds by 25%

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